Tschermakite

tschermakite

zoisite

pargasite

tremolite

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Formula: ☐Ca₂(Mg₃Al₂)(Si₆Al₂)O₂₂(OH)₂
Inosilicate (chain silicate)
Crystal System: Monoclinic
Specific gravity: 3.15 measured, 3.25 calculated
Hardness: 5 to 6
Streak: Pale grey-green
Colour: Medium green to dark green to green-black to black, rarely brown
Common impurities: Ti,Mn,Na,K,H₂O,Fe
Environments:

Igneous environments
Metamorphic environments

Tschermakite occurs in eclogites and other ultramafic igneous rocks, and in medium- to high- grade metamorphic rocks, typically amphibolite (HOM). Kyanite and garnet are common associates (HOM, Mindat).

Alteration:

magnesium-rich tremolite, tschermakite and albite to pargasite and quartz
☐Ca₂Mg₅Si₈O₂₂(OH)₂ + ☐Ca₂(Mg₃Al₂)(Si₆Al₂)O₂₂(OH)₂ + 2Na(AlSi₃O₈) ⇌ 2NaCa₂(Mg₄Al)(Si₆Al₂)O₂₂(OH)₂ + 8SiO₂
(AM 92.4.491)

magnesium-rich tremolite, zoisite, corundum and H₂O to tschermakite
3☐Ca₂MgSi₈O₂₂(OH)₂ + 2Ca₂Al₃[Si₂O₇][SiO₄]O(OH) + 7Al₂O₃ + H₂O ⇌ 5☐Ca₂(Mg₃Al₂)(Si₆Al₂)O₂₂(OH)₂
(AM 76.990)

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